Most vehicles in operation today are powered by internal combustion (IC) engines. Internal combustion engines typically have multiple cylinders or other working chambers where combustion occurs. The power generated by the engine depends on the amount of fuel and air that is delivered to each working chamber.
Fuel efficiency of internal combustion engines can be substantially improved by varying the engine displacement. This allows for the full torque to be available when required, yet can significantly reduce pumping losses and improve thermal efficiency by using a smaller displacement when full torque is not required. The most common method today of implementing a variable displacement engine is to deactivate a group of cylinders substantially simultaneously. In this approach the intake and exhaust valves associated with the deactivated cylinders are kept closed and no fuel is injected when it is desired to skip a combustion event. For example, an 8 cylinder variable displacement engine may deactivate half of the cylinders (i.e. 4 cylinders) so that it is operating using only the remaining 4 cylinders. Commercially available variable displacement engines available today typically support only two or at most three displacements.
Another engine control approach that varies the effective displacement of an engine is referred to as “skip fire” engine control. In general, skip fire engine control contemplates selectively skipping the firing of certain cylinders during selected firing opportunities. Thus, a particular cylinder may be fired during one engine cycle and then skipped during the next engine cycle and selectively skipped or fired during the next. In this manner, even finer control of the effective engine displacement is possible. For example, firing every third cylinder in a 4 cylinder engine would provide an effective reduction to ⅓rd of the full engine displacement, which is a fractional displacement that is not obtainable by simply deactivating a set of cylinders to create an even firing pattern. Similarly, firing every other cylinder in a 3 cylinder engine would provide an effective displacement of ½, which is not obtainable by simply deactivating a set of cylinders.
U.S. Pat. No. 8,131,445 (which is incorporated herein by reference) teaches a continuously variable displacement engine using a dynamic skip fire operational approach, which allows any fraction of the cylinders to be fired on average using individual cylinder deactivation. In a continuously variable displacement mode operated in skip-fire, the amount of torque delivered generally depends heavily on the firing fraction, or fraction of combustion events that are not skipped. In other skip fire approaches a particular firing pattern or firing fraction may be selected from a set of available firing patterns or fractions.
In order to operate with dynamic skip fire control it is necessary to control the intake and exhaust valves in a more complex manner than if the cylinders are always activated. Specifically the intake and/or exhaust valves remain closed during a skipped working cycle to minimize pumping losses. This contrasts with an engine operating on all cylinders, where the intake and exhaust valves open and close on every working cycle. Most vehicles in operation today use a camshaft to open and close the intake valves. The valve train may incorporate a cam phaser to control the timing of the valve opening and closing relative to the crankshaft. Some cam operated engines also have adjustable valve lift. For example, some engines have mechanisms to shift valves between a “high lift” and “low lift” level; for example, a maximum lift of 11 mm for “high lift” and of 4 mm for “low lift”. As an alternative to cam controlled valves, some engines use electronic valve actuation, which has more flexibility in the valve opening and closing because the valve motion is not constrained by camshaft rotation.
For cam operated valves a method to deactivate a valve is to incorporate a collapsible valve lifter into the valve train. To activate the valve the lifter remains at its full extension and to deactivate the valve the lifter collapses failing to transfer the cam lobe profile to the valve. Valve activation/deactivation is controlled by a solenoid which deactivates the valve by providing high pressure oil to the collapsible lifter. Other mechanisms exist to deactivate valves in engines with cam operated valves.
U.S. patent application Ser. Nos. 14/487,563, 14/582,008, and 14/700,494, each of which is incorporated herein by reference in their entireties, teach methods of sensing failures of an exhaust valve to open after a combustion event. As pointed out in these applications, failure of the exhaust valve to open will result in high pressure combustion gases being trapped in the cylinder, which can lead to damage of the intake valve and its associated mechanism if it attempts to open against this high pressure.
Failures of an intake valve to activate or deactivate under skip fire control can also have a deleterious impact on engine operation. Failure of the intake valve to open will result in missing a planned firing event. This may lead to unburnt hydrocarbons being transmitted to the engine exhaust and may result in unacceptable emissions. There will also be a loss of engine torque and increased engine roughness. Failure of an intake valve to close may result in increased pumping losses and excess oxygen in the exhaust gases deleteriously impacting the catalytic converter. Failures in the cam adjustment mechanism can also lead to emission and engine performance issues. In all cases information regarding intake valve or cam failures may be required to be communicated to a vehicle on-board diagnostic (OBD) system to satisfy governmental regulations, such as those imposed by the California Air Resources Board (CARB). It is thus desirable to make a determination of whether actual cylinder air induction accurately matches the commanded operation.